There are no sure things in the NFL. Although Steven Jackson looked as healthy and spry as ever for the Rams last season, he’s still a running back with 2,802 career touches going on 30 years of age.

With that out of the way...Jackson looked as healthy and spry as ever for the Rams last season. That was for an offense that needed Jackson to bang out 4.1 yards per carry just to have any chance of getting into field goal range. It meant that for the fifth time in six years, one of the preeminent power backs of his generation was held to six or fewer total touchdowns.

Things are going to be different in Atlanta. That broken down jalopy the Falcons called Michael Turner? He got 51 red zone touches last season. He scored 10 rushing touchdowns for the fifth consecutive year. Turner’s touch and TD totals would have been even more massive had he had anything left at all.

Jackson, meanwhile — who is twice the player Turner is at this stage of their respective careers — got the ball just 27 times inside the 20, and totaled only four touchdowns. Those numbers could have easily been doubled had he been playing for an offense like the Falcons’.

As 2012 proved, the Falcons and Jackson need each other. Atlanta needs Jackson to move the chains and provide competency as a battering ram. Jackson needs Atlanta to show he wasn’t just racking up good numbers — besides touchdowns, of course — on bad teams all those years in St. Louis.

It’s a marriage that makes perfect sense on paper, and one that should yield all the scores the Falcons and fantasy owners could ever desire provided S-Jax doesn’t break down all at once.

“Lost” is a tough word in this instance, because it’s not as if Welker isn’t going to stuff the stat-sheet in one of the league’s most fearsome offenses. It’s just that the presence of Demaryius Thomas and Eric Decker is going to make it close to impossible for Welker to even approach the 112 catches he averaged his six seasons in New England.

75-85 is far more realistic, and while 80 grabs would still put Welker near the top of the league in receptions, it’s no secret that the key to his fantasy success has been snagging more balls than anyone else in football.

Welker is going to soak up targets and catches, but whereas his place in the Patriots offense made him the rare slot receiver to flirt with WR1 status, he’s going to be much closer to a WR3 in Denver’s well-oiled machine. That’s still valuable, but far from elite.

Cook may be the shakiest proposition on this list. Although part of his underachievement in Tennessee was undeniably due to misapplication by the coaching staff, there’s no escaping that he caught just 131 passes in four seasons, and never distinguished himself as a blocker.

But the fact that Cook became one of the hottest names on the market just minutes after free agency opened tells you a lot. Cook — all 6-foot-5, 248 pounds of him — has the potential to be special, and a Rams offense intent on getting more explosive in 2013 is going to give him every opportunity to stretch the seams.

In many ways, Cook will be replacing Danny Amendola as Sam Bradford’s slot receiver. It’s a position Bradford has rained targets upon since the minute he came into the league, and will give Cook the opportunity to shatter the career-best 49 catches he posted in 2011.

Cook requires a leap of faith, but if you take it, you could be rewarded with one of 2013’s most improved players.

It’s not just that Lloyd is leaving the Patriots offense. It’s that he’s been turned out by his muse Josh McDaniels

A chronic underachiever before he became a late-bloomer under McDaniels, Lloyd is being parted from the only coach he’s ever known true success under after a winding three years in three different cities.

Going on 33 with a burgeoning reputation as a headcase, Lloyd is not headed for greener pastures, and could have trouble even finding someone willing to put up with him. Couple that with physical skills that were in obvious decline last season, and you have a player whose unlikely late-career renaissance should be ending after three seasons.

With the meat and potatoes portion of free agency in the books, now is the time to take a look at four players who have gained value since March 12, and four who have lost it.

There are no sure things in the NFL. Although Steven Jackson looked as healthy and spry as ever for the Rams last season, he’s still a running back with 2,802 career touches going on 30 years of age.

With that out of the way...Jackson looked as healthy and spry as ever for the Rams last season. That was for an offense that needed Jackson to bang out 4.1 yards per carry just to have any chance of getting into field goal range. It meant that for the fifth time in six years, one of the preeminent power backs of his generation was held to six or fewer total touchdowns.

Things are going to be different in Atlanta. That broken down jalopy the Falcons called Michael Turner? He got 51 red zone touches last season. He scored 10 rushing touchdowns for the fifth consecutive year. Turner’s touch and TD totals would have been even more massive had he had anything left at all.

Jackson, meanwhile — who is twice the player Turner is at this stage of their respective careers — got the ball just 27 times inside the 20, and totaled only four touchdowns. Those numbers could have easily been doubled had he been playing for an offense like the Falcons’.

As 2012 proved, the Falcons and Jackson need each other. Atlanta needs Jackson to move the chains and provide competency as a battering ram. Jackson needs Atlanta to show he wasn’t just racking up good numbers — besides touchdowns, of course — on bad teams all those years in St. Louis.

It’s a marriage that makes perfect sense on paper, and one that should yield all the scores the Falcons and fantasy owners could ever desire provided S-Jax doesn’t break down all at once.

“Lost” is a tough word in this instance, because it’s not as if Welker isn’t going to stuff the stat-sheet in one of the league’s most fearsome offenses. It’s just that the presence of Demaryius Thomas and Eric Decker is going to make it close to impossible for Welker to even approach the 112 catches he averaged his six seasons in New England.

75-85 is far more realistic, and while 80 grabs would still put Welker near the top of the league in receptions, it’s no secret that the key to his fantasy success has been snagging more balls than anyone else in football.

Welker is going to soak up targets and catches, but whereas his place in the Patriots offense made him the rare slot receiver to flirt with WR1 status, he’s going to be much closer to a WR3 in Denver’s well-oiled machine. That’s still valuable, but far from elite.

Cook may be the shakiest proposition on this list. Although part of his underachievement in Tennessee was undeniably due to misapplication by the coaching staff, there’s no escaping that he caught just 131 passes in four seasons, and never distinguished himself as a blocker.

But the fact that Cook became one of the hottest names on the market just minutes after free agency opened tells you a lot. Cook — all 6-foot-5, 248 pounds of him — has the potential to be special, and a Rams offense intent on getting more explosive in 2013 is going to give him every opportunity to stretch the seams.

In many ways, Cook will be replacing Danny Amendola as Sam Bradford’s slot receiver. It’s a position Bradford has rained targets upon since the minute he came into the league, and will give Cook the opportunity to shatter the career-best 49 catches he posted in 2011.

Cook requires a leap of faith, but if you take it, you could be rewarded with one of 2013’s most improved players.

It’s not just that Lloyd is leaving the Patriots offense. It’s that he’s been turned out by his muse Josh McDaniels

A chronic underachiever before he became a late-bloomer under McDaniels, Lloyd is being parted from the only coach he’s ever known true success under after a winding three years in three different cities.

Going on 33 with a burgeoning reputation as a headcase, Lloyd is not headed for greener pastures, and could have trouble even finding someone willing to put up with him. Couple that with physical skills that were in obvious decline last season, and you have a player whose unlikely late-career renaissance should be ending after three seasons.

Bush’s career hasn’t followed a straight line. The forbearer to Darren Sproles in New Orleans, Bush’s post-lockout trade to the Dolphins was derided as a ticket-selling stunt in some quarters.

Then the former No. 2 pick went out and not only managed to have his healthiest season since his rookie year, but to post his first 1,000-yard campaign at the age of 26. A lingering knee issue helped keep Bush 14 yards shy of his second straight 1K-effort in 2012, but the point had been made. No, Bush is not a prototypical between-the-tackles dynamo. Yes, he’s a damn useful player, one capable of helping via both land and air.

Bush may not match the 222 carries he averaged the past two seasons, but he’s going to blow away the 2.5 weekly catches he managed with the Dolphins, and is a major threat to lead all backs in receptions.

He’s the exact kind of movable chess piece the Lions’ offense has lacked since concussions cut short Jahvid Best’s career, and should take pressure off QB Matthew Stafford, who far too often had to drop back against defenses who knew he was passing last season.

Health is still the biggest question mark with Bush, but now older and wiser than the player who missed 20 games his final four years in New Orleans, he appears to have learned what it takes to stay on the field. A legitimate threat for RB1 value in PPR formats, Bush will flirt with high-end RB2 status in standard leagues.

If Bush is gaining value in Detroit, that means someone else is losing it. In this case, it’s two someones. There’s no question Bush’s arrival means Leshoure won’t approach the 215 carries he notched last season — 215 uninspiring, plodding carries — but it will be Bell whom Bush hurts the most.

Bell quietly racked up 52 receptions last season, which was fifth amongst all running backs. It made him a PPR dark horse, and a pale imitation of a playmaker for an offense that lacked one outside of Calvin Johnson. Now Bell will be a pure backup, mostly glued to the sideline as Bush challenges for the league lead in catches among backs.

Leshoure may be able to retain more of his value than he deserves if he continues to see snaps near the goal-line, but Bush is going to take a major bite out of both backs who tried, and ultimately failed, to sustain the Lions’ rushing attack last season.

First things first: Tannehill was probably going to gain value regardless of what the Dolphins did with his supporting cast. It’s what most properly developing first-round quarterbacks do. But Mike Wallace and Dustin Keller? They’re not going to hurt.

That’s not to say Tannehill is primed to make the leap to QB1 status. This is still a player who’s made just 35 total starts at quarterback since he graduated high school. But the Dolphins have avoided the biggest mistake the Rams made with Sam Bradford, and loaded their QB of the future up with proven weapons instead of making him tough out his progression with third- and fourth-round fliers.

Tannehill made it clear as a rookie he has the talent to stay at this NFL thing for a long time. Now he has a receiver corps that will aid him in the next step.

Let’s just say the past 15 months weren’t foreboding ones for a player who will turn 30 in September. That his 11 missed games were no big deal. That his knee, head, abdominal, ankle and groin injuries were nothing to worry about.

With a quarterback who hasn’t proven capable of delivering the ball and a “supporting cast” at receiver that’s going to have trouble drawing attention away from him, Jennings is going to be attempting to prove his career isn’t on the downslope under the toughest of circumstances.

Maybe a pair of hot finishes last season — both Jennings and Ponder’s — tell the story of what to expect in 2013. But the larger picture is much more ominous, one that suggests not only is Jennings’ best quarterback behind him, but his best days, as well.